Metro-Access Convergence

Large optical networks are typically partitioned into core (inter-city) and metro (intra-city) sub-networks, and the last portion of the telecommunications network that runs the services to the home or business is the access network. The technologies for core, metro and access sub-networks will provide rapid provisioning of connections within each sub-network (Fig. 7.1). However, it is essential that the core, metro and access sub-networks are able to work interconnected to release the fast provisioning potential of these sub-networks, since a large part of the anticipated connections will need to traverse both core and metro sub-networks and finally reach the access. This requires signalling and routing information exchange between the different sub-networks. The inter-networking, and particularly the routing information exchange, is the focus of the core-metro-access interfacing.

While access and metro sub-networks handle local traffic and offer servicesensitive aggregation and service-specific features, the core network transports relatively homogeneous connections across long distances, thus the core network may be based on different technology than the access and metro sub-networks. Due to this fact, simpler optical nodes based on low cost or functionality may be used in access and metro transport whilst long-haul networks may involve high performance on the optical spectral characteristics of the devices. These differences may result in some specific requirements on the routing information that need to be distributed within the core, metro and access sub-networks. However, there are fundamental requirements on the routing information that needs to be exchanged between the sub-networks [Wang01].